How to disable Pie menu when holding TAB in Blender 2.8?
Adjusting this is the same as previous versions, although the pie menu names have changed in 2.80 due to them becoming a permanent part of blender.

Before changing the key bindings, try adjusting the drag threshold, this will allow more movement before it considers you are dragging. This will be applied throughout blender, not just the mode menu.



If you still want to change the key bindings, you can use the filter to find key-binding entries that use the tab key.



You can then see the settings that are in place, you may want to delete the Call Pie Menu or assign it to a different shortcut, I use &#9096; Ctrl&#8633; Tab to bring up a mode menu.